The application claims benefit of Japanese Application No. Hei 11-220436 filed in Japan on Aug. 3, 1999, the contents of which are incorporated by reference.
1. Field of the Invention
The present invention relates to an image display device, and in particular to an image display device for increasing the apparent number of pixels by pixel-staggering.
2. Related Art Statement
Hitherto, image display devices using a CRT have been widely used. In recent years, however, the market share of image display devices using a liquid crystal display element or the like has been expanding.
In such image display devices, the exactitude of a displayed image is basically decided by the number of pixels constituting the liquid crystal display element. If the pixel number is increased to obtain a highly exact image, costs ill the liquid crystal display element rise or a higher-speed signal processing circuit becomes necessary.
Thus, there are developed techniques for displaying a more exact image, using a liquid crystal display element whose pixel number is limited.
One example of such a technique is increasing the apparent number of pixels by performing pixel-staggering operation called wobbling, in which the optical axis of light from a liquid crystal display element is vibrated toward a given direction.
Examples of this wobbling technique include two-point pixel-staggering technique wherein apparent pixel positions are shifted in an even number field and an odd number field, and four-point pixel-staggering technique wherein each of the fields is further divided into two sub-fields and apparent pixel positions are shifted in each of these sub-fields.
For example, Japanese Unexamined Patent Publication No. Hei 4-63332 discloses a method for improving solution of a liquid crystal display panel, using two combinations of a liquid crystal panel for controlling the direction of polarized light and a crystal plate, and 4 frame memories. The method disclosed therein involves shifting an image by a xc2xd pixel pitch in the horizontal direction by a combination of the liquid crystal panel for controlling the direction of polarized light and the crystal plate, and shifting the image by a xc2xd pixel pitch in the vertical direction by means of the other combination of the liquid crystal panel for controlling the direction of polarized light and the crystal plate. In this manner, four-point pixel-staggering is performed to improve resolution. That is, 4 fields constitute one frame, and an image is divided into 4 images. The respective division images are memorized in the frame memories. In the first field, the division image is caused to go straight in the two liquid crystal panels and displayed. In the second field, the division image is shifted in the horizontal direction by a xc2xd pixel pitch and displayed. In the third field, the division image is shifted to the vertical direction by a xc2xd pixel pitch and displayed. In the fourth field, the division image is shifted in the horizontal and vertical directions by xc2xd pixel pitches, respectively, and displayed. By synthesizing these images, a highly exact image based on 4-point pixel-staggering is displayed.
Japanese Unexamined Patent Publication No. Hei 7-36054 discloses an optical device having two one-dimensional two-point pixel-staggering elements composed of a liquid crystal phase modulating element and a birefringence medium. The one element is laminated on the other element in such a manner that the former is positioned at a rotation angle of 90xc2x0 from the latter around the axis of incident light. Inside one frame or one field, pixel-staggering is performed 4 times in vertical and horizontal directions. In this way, this device uses two-dimensional four-point pixel-staggering to make its resolution high.
Concerning an image display device using the four-point pixel-staggering, the Applicant developed a technique wherein pixels to be staggered are not positioned at respective apexes of a rectangle but are positioned at respective apexes of a parallelogram to improve resolution in both horizontal and vertical directions. This technique is described in Japanese Patent Application No. Hei 10-336482, which has not yet been opened to the public.
The technique as described in Japanese Patent Application No. Hei 10-336482 has the advantage that the apparent pixel density over the whole of an image is made high except peripheral portions of a screen to improve exactitude of the image. However, for example, at right and left ends of peripheral portions of the screen, areas whose apparent pixel density is thin are inconveniently generated such that resolution cannot be improved. Only the right and left ends of the peripheral portions display partial images which are poorer in exactitude than other areas, for example, the central area of the screen. Regardless of the fact that areas having partial images whose exactitude is low are only a little in the whole and further these areas are at the right and left areas, such an image causes a drop in ease of watching the screen for users.
An object of the present invention is to provide an image display device that makes it possible to watch easily a more exact image through a limited number of pixels.
A first aspect of the present invention is an image display device comprising a display element in which plural pixels are arranged, pixel-staggering means for sequentially changing optical paths of beams emitted from the respective pixels of the display element, and mask means for prohibiting image-display at peripheral areas where apparent density of the pixels is thin when pixel-staggering is performed by the pixel-staggering means.
A second aspect of the present invention is an image display device comprising a display element in which plural pixels are two-dimensionally arranged, image processing means for controlling in the display element for each pixel to display an image on the basis of image signals, optical path changing means for sequentially refracting optical paths of beams emitted from the display element to perform pixel-staggering, and mask means for displaying end areas in at least one direction of the horizontal direction and end areas in the vertical direction in black when pixel-staggering is performed by the optical path changing means.
These object(s) and advantages of the present invention will become further apparent from the following detailed explanation.